1. Field of the Invention
The present invention relates to a semiconductor memory device, such as Dynamic Random Access Memory (DRAM) and static Random Access Memory (SRAM), particularly to a semiconductor memory device employing a voltage noise reduction system therein to reduce voltage noises generated by the internal circuit thereof.
2. Description of the Related Art
A semiconductor memory device having voltage a noise reduction system, for example, is disclosed in the Japanese Laid-open patent publication No. 60-206161, published on Oct. 17, 1985, of which the entire disclosure is incorporated herein by reference.
The disclosed noise reduction system in the above mentioned publication, as disclosed in FIG. 1 thereof (not shown in this specification), employs a first level aluminum layer 10 formed on a silicon dioxide (SiO.sub.2) layer 7 substantially covering the main surface of a semiconductor substrate 1, a dielectric (SiO.sub.2, Nitride or Ta.sub.2 O.sub.5) layer 12 formed on the first level aluminum layer 10 and a second level aluminum layer 11 formed on the dielectric layer 12 so as to form a composite layer of the first level aluminum, dielectric and second level aluminum layers 10, 12 and 11. The first level aluminum layer 10 supplies the drain region 2 of a transistor in FIG. 1 with a supply voltage while the second level aluminum layer connects the source region 3 of the transistor to the ground. Therefore, the disclosed noise reduction system can reduce voltage noises generated by the external or internal circuits of a semiconductor device since the composite layer 10, 12 and 11 employs capacitance formed between the first and second level aluminum layers 10 and 11. However this noise reduction system requires the relatively complex pattern layout for other circuits of the semiconductor memory device and, further, the additional metal layer forming process to form the second level aluminum layer (Vss Line) right over the first level aluminum layer (Vcc line) after the dielectric layer being formed on the first level aluminum layer in order to form the composite layer.